The present invention relates to positioning in a mobile telecommunication network. A network supporting positioning is able to keep track of the position of the mobile terminals, also referred to as user equipment (UE) that are served by said network. Positioning is a feature offered by a mobile telecommunication network to support location-based services which is one of the most important applications of 3G networks.
In FIG. 1, a Universal Mobile Telephony System (UMTS) is depicted. The UMTS network comprises a Core Network (CN) 100 that is connectable to other networks such as the Internet, other mobile networks e.g. GSM systems and fixed telephony networks denoted POTS in FIG. 1. The CN 100 connects to a plurality of Radio Network Controllers (RNCs) 102 via a Iu interface 101. One RNC 102 is connected to another RNC 102 by another interface, the Iur interface 103. Furthermore, the respective RNC 102 controls a plurality of Node-Bs 104 comprising one or more base stations 106 that is connected to the RNC by means of the Iub interface 105. Each base station covers an area, i.e. a cell and is arranged to serve the mobile terminals within said cell. Finally, the mobile terminals 108, also referred to as User Equipments (UE) are connected to one or
The present invention relates to all mobile telecommunication systems that comprises an interface, such as an Iur interface, between the radio network controlling units of the system. Thus, the present invention is not limited to a UMTS system and the protocols as described.
A comparatively simple method for providing positioning is to apply an identity of the cell, e.g. the cell-ID, and more precisely a description of the geographical area covered by the cell, e.g. the Geographical Area Information (GAI), that is related to the cell-ID, to retrieve the location of the UE. The GAI identifies the geographical area of a cell and is represented by a polygon. This implies that the location of a UE 108 can be determined by identifying the cells, or one of the cells, where the UE 108 is currently located and by associating the identity of the cell or cells with the GAI. It exists signalling support for this method over the Iur-interface in UMTS Terrestrial Radio Access Network (UTRAN), while it is assumed that signalling support over the Iub-interface is not required since each controlling-Radio Network Controller (C-RNC) should have extensive knowledge of the cells that it controls. The UTRAN interfaces Iur and Iub as well as the C-RNC will be further described below. That results in that the coverage area of the cell is mapped on geographical coordinates and the precision of the position of the UE is limited to the area of the cell.
More advanced solutions would be to adopt more complex positioning methods such as Observed Time Difference Of Arrival (OTDOA) or Assisted Global Positioning System (A-GPS). The main drawback for both of these solutions is their inherent complexity at implementation in a mobile communication system. Both A-GPS and OTDOA require GPS receivers in the network, and new measurements are required. Another drawback with A-GPS is that it may not work in indoor scenarios due to poor coverage of the satellites. Furthermore, OTDOA requires a sufficiently high number of node-B pairs available in order to achieve good accuracy of the position, since the UEs measure the relative timing difference between pairs of Node Bs. The accuracy of the position increases with the number of measurements. Another drawback is that a UE only can listen to one UE at a time. Good accuracy can thus theoretically be obtained by using idle periods in the downlink (IPDL). However, implementation of IPDL has hardware impacts and adds further complexity to the method.
Moreover, there is a tendency to design modern communication networks as distributed systems, which inter alia implies a distinction between network resources on the one hand and communication connections on the other hand. Resources may refer to, e.g., the various hardware components that are applied, and, for CDMA-based communication systems, the transmission power level and channelisation codes. In such systems it is common that different logical as well as physical units control different parts of the network. One unit is e.g. responsible for the control of a communication connection while another unit is responsible for the control of the resources that said communication connections use. This will now be illustrated by means of FIG. 1. The FIG. 1 shows a part of a UMTS Terrestrial Radio Access Network (UTRAN) 10, which can serve as an example of a distributed network as described above. Radio Network Controllers (RNC) 102a, 102b perform the control of communication connections and network resources respectively of the base stations 104a–104d and are responsible to provide connections to the Core Network 100. The RNCs 102a, 102b are connected to Node-B:s 104a–104d, wherein one Node-B comprises one or more radio base stations 106. Each base station 106 controls the UEs within its covered cell area. Due to the above-mentioned distinction, the RNC can have various roles: Regarding network resources, the RNC 102b acts as a controlling RNC (C-RNC) that is responsible for the control of resources of a part of said network including a number of cells, each of which serving a plurality of UEs 108. Regarding the communication connections, an RNC 102a, 102b acts as the serving RNC (S-RNC) for those connections that terminates in that RNC. However, when a UE 108 moves during an ongoing session from a first RNC 102a, which is the S-RNC for the corresponding communication connection, to a neighbouring RNC 102b, the original RNC 102a still remains the S-RNC for this connection while the second RNC 102b, which is in control of the resources that this connection uses, is a drift RNC (D-RNC) that supports the S-RNC 11a with the necessary radio resources; however, without any influence on said connection. Thus, the D-RNC controls at least one cell that is used in a radio connection controlled by a serving RNC and supplies the S-RNC with resources.
Thus, it is a problem, as previously described, that positioning information, that only is based on the cell-ID, is not accurate enough and may hence imply disadvantages for services where a more exact location of the UEs is required.
Another problem is that a S-RNC cannot get sufficient positioning information of a UE that has roamed during an ongoing session to a D-RNC, which provides network resources for said UE, while the S-RNC still controls the connection of said UE.